Make emission shader emit straight rays
That's not something you can do AFAIK. You could try to block out the feathering of the light with a shadow created by another mesh aperture, but even then you have to deal with diffraction of light around the corners. That just isn't how light works. 

For example, see this monochromatic light that diffracts when passing through a small aperture:



I'd suggest you look at the rest of the Wikipedia article where that image came from.

The Cycles behavior is relatively consistent (although it appears to only have the central diffraction maxima):





As far as the amount of light spread, you may be interested in the lamp size property. From the Blender manual:


  Size of the lamp in Blender Units; increasing this will result in softer shadows and shading.